Broadband Properties of Blazars

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Broadband Properties of Blazars
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• Markus Böttcher
• Ohio University, Athens, OH, USA

• Phenomenology of Blazars
• Recent Observational Results on 3C66A and 3C279
• Models of Blazar Emission

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Blazars
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• Class of AGN consisting of BL Lac objects and
  gamma-ray bright quasars
• Rapidly (often intra-day) variable
• Strong gamma-ray sources
• Radio jets, often with superluminal motion
• Radio and optical polarization

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The Blazar Sequence
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Low-frequency peaked BL Lacs (LBLs) Peak
frequencies at IR/Optical and GeV
gamma-rays Intermediate overall
luminosity Sometimes g-ray dominated
Collmar et al. (2006)
High-frequency peaked BL Lacs (HBLs) Low-frequenc
y component from radio to UV/X-rays, often
dominating the total power High-frequency
component from hard X-rays to high-energy
gamma-rays
Flat-Spectrum Radio Quasars Low-frequency
component from radio to optical/UV High-frequency
component from X-rays to g-rays, often dominating
total power Peak frequencies lower than in BL Lac
objects
(Boettcher Reimer 2004)
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The Multiwavelength Campaign on 3C66A
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Radio obs. by UMRAO (Univ. of Michigan),
Metsähovi (Finland), VLBA,
Optical observations by the WEBT collaboration
24 observatories in 15 countries around the world
IR observations by Mt. Abu (India) NOT (Canary
Islands), Campo Imperatore (Italy)
Very-high-energy gamma-ray obs.
by Whipple/VERITAS (Arizona), STACEE (New Mexico)
VHE
X-ray obs. by RXTE
RXTE
(Böttcher, et al., 2005)
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Broadband Spectral Energy Distributions
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Synchrotron peak at optical wavelengths
Synchrotron emission extends far into the X-ray
regime (gt 10 keV)
Estimates from spectrum and variability
Variability ? Size Rb 2.21015 D1 cm
Synchrotron luminosity ? B 4.4 D1-1 G
Synchrotron spectral index ? Electron injection
index q 3
? Particle acceleration at non-parallel shocks
Synchrotron peak frequency ? ge,min 3.1103
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Radio Observations
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Rather smooth jet without clearly visible knots
Identification of 7 jet components
(T. Savolainen)
Evidence for superluminal motion in only one
component vapp (12 8.0) c
Decay of Brightness Temperature TB with distance
d from the core TB d-2 ? B d-1
Predominantly perpendicular magnetic field!
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The Multiwavelength Campaign on 3C279 in
Jan./Feb. 2006
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• INTEGRAL Chandra ToO observations
• Coordinated with WEBT radio, near-IR, optical
  (UBVRIJHK)
• Triggered by Optical High State (R lt 14.5) on
  Jan. 5, 2006
• Addl. X-ray Observations by Swift XRT

Preliminary
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The Multiwavelength Campaign on 3C279 in
Jan./Feb. 2006
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• X-ray/g-ray observations during a period of
  optical-IR-radio decay

Preliminary

• Minimum at X-rays seems to precede optical/radio
  minimum by 1 day.

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The Multiwavelength Campaign on 3C279 in
Jan./Feb. 2006
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• SED (Jan 15, 2006) basically identical to low
  states in 92/93 and 2003 in X-rays
• High flux, but steep spectrum in optical
• Indication for cooling off a high state?
• Did we miss the HE flare?

Analysis is in progress
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Blazar Models
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Synchrotron emission
Relativistic jet outflow with G 10
Injection, acceleration of ultrarelativistic
electrons
nFn
n
Compton emission
g-q
Qe (g,t)
nFn
Leptonic Models
g
g2
g1
n
Injection over finite length near the base of the
jet.
Seed photons Synchrotron (within same region
SSC or slower/faster earlier/later emission
regions decel. jet), Accr. Disk, BLR, dust
torus (EC)
Additional contribution from gg absorption along
the jet
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Blazar Models
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Proton-induced radiation mechanisms
Injection, acceleration of ultrarelativistic
electrons and protons
Relativistic jet outflow with G 10
nFn
g-q
Qe,p (g,t)
n

• Proton synchrotron

g
g2
g1

• pg ? pp0 p0 ? 2g

Synchrotron emission of primary e-

• pg ? np p ? mnm
• m ? enenm

? secondary m-, e-synchrotron
Hadronic Models
nFn

• Cascades

n
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Modeling of 3C66A in 2003-2004
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Time-dependent broadband SED
Model parameters D G 24 RB 3.61015 cm B
2.4 G q 3.1 ? 2.4 g2 3.0104 ? 4.5104 Linj
2.71041 erg/s ? 7.01041 erg/s
(Joshi Böttcher 2006, in prep.)
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Modeling of 3C66A in 2003-2004
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R-band (optical) light curve
Model parameters D G 24 RB 3.61015 cm B
2.4 G q 3.1 ? 2.4 g2 3.0104 ? 4.5104 Linj
2.71041 erg/s ? 7.01041 erg/s
Hardening of injection spectrum during flare
increase of high-energy cut-off ? Flaring caused
by changing magnetic-field orientation?
(Joshi Böttcher 2006, in prep.)
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Spectral modeling results along the Blazar
Sequence Leptonic Models
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High-frequency peaked BL Lac (HBL)
Low magnetic fields ( 0.1 G) High electron
energies (up to TeV) Large bulk Lorentz factors
(G gt 10)
Synchrotron
SSC
No dense circumnuclear material ? No strong
external photon field
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Spectral modeling results along the Blazar
Sequence Leptonic Models
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Radio Quasar (FSRQ)
High magnetic fields ( a few G) Lower electron
energies (up to GeV) Lower bulk Lorentz factors
(G 10)
External Compton
Plenty of circumnuclear material ? Strong
external photon field
Synchrotron
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Spectral modeling results along the Blazar
Sequence Hadronic Models
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HBLs
Low co-moving synchrotron photon energy density
high magnetic fields high particle energies ?
High-Energy spectrum dominated by featureless
proton synchrotron initiated cascades, extending
to multi-TeV, peaking at TeV energies
LBLs
Higher co-moving synchrotron photon energy
density lower magnetic fields lower particle
energies ? High-Energy spectrum dominated by pg
pion decay, and synchrotron-initiated cascade
from secondaries ? multi-bump spectrum extending
to TeV energies, peaking at GeV energies
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The Blazar Sequence
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NOT a prediction of leptonic or hadronic jet
models!
Variations of B, ltggt, G, chosen as free
parameters in order to fit individual objects
along the blazar sequence.
Consistent prediction Strong gt 100 GeV emission
from LBLs, FSRQs are only expected in hadronic
models!
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Summary
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• Blazar SEDs successfully be modelled with both
  leptonic and hadronic jet models.
• Possible multi-GeV - TeV detections of LBLs or
  FSRQs and spectral variability may serve as
  diagnostics to distinguish between models.
• Both leptonic and hadronic models provide
  plausible scenarios for explaining the blazar
  sequence, but the blazar sequence is not a
  prediction of either type of models.

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Time-dependent leptonic blazar modeling
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• Solve simultaneously for evolution of electron
  distribution,

?ne (g,t)
.
______
__
?
ne (g,t)
______
- (g ne) Qe (g,t) -
?t
?g
tesc,e
rad. adiab. losses
el. / pair injection
escape
and co-moving photon distribution,
?nph (e,t)
.
.
_______
nph (e,t)
______
nph,em (e,t) nph,abs (e,t) -
?t
tesc,ph
Sy., Compton emission
SSA, gg absorption
escape